AE表达式｜32、如何将表达式链接到外部文件或JSON文件？

1、怎样链接到问层？

eval() 函数计算 JavaScript 字符串，并把它作为脚本代码来执行。

如果参数是一个表达式，eval() 函数将执行表达式。如果参数是Javascript语句，eval()将执行 Javascript 语句。

eval(拾取器拾取文本图层到SourceText.value)

例如：

eval(thisComp.layer("myText").text.sourceText.value)

2、怎样引用外部txt文件？
新建txt文件，保存。

myPath = “txt文件位置”; //引用文件位置
val = $.evalFile(myPath); //引用外部文件中的js
[val,val] // 将结果放入数组中

3、怎样链接JSON文件？
JSON(JavaScript Object Notation, JS 对象简谱) 是一种轻量级的数据交换格式。

To work with a standard JSON file, use the following steps:

Select File > Import.

To import, select a .JSON file and click Open.

The file is added to your project window. Create a composition with the footage.

Add a solid to the composition. To add a solid, select Layer > Solid.

In the Timeline panel, twirl open the properties of the solid layer and Alt+Click the Opacity parameter.

Change the data in the expression to modify your animation. You can control the JSON data and the data is referenced from the data file where all the information is stored.

You can also replace the JSON file with another JSON file to change the data being referenced. To replace, select Replace Footage > File, and open the new file from your computer.

To use the data, you can apply an expression on the property you wish the data to drive, then:

Use the sourceData attribute to read the data in a .JSON file. For example:

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var sampleData = footage("sample.json").sourceData;

To return its value, reference the specific property inside the JSON data. For example,

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myData.engineData.RPM or myData.latitude.value.

例如有这样一个JSON文件Exanmle JSON File.json,其内容为：

{
    "planet": {
        "mercury": {
            "name": "Mercury",
            "radius": 2439.7,
            "distance": {
                "perihelion": 46001200,
                "aphelion": 69816900
            },
            "gravity": 0.380
        },
        "venus": {
            "name": "Venus",
            "radius": 6051.8,
            "distance": {
                "perihelion": 107477000,
                "aphelion": 108939000
            },
            "gravity": 0.904
        },
        "earth": {
            "name": "Earth",
            "radius": 6378.1,
            "distance": {
                "perihelion": 147095000,
                "aphelion": 152100000
            },
            "gravity": 1.000
        },
        "mars": {
            "name": "Mars",
            "radius": 3389.5,
            "distance": {
                "perihelion": 206654500,
                "aphelion": 249230000
            },
            "gravity": 0.376
        },
        "jupiter": {
            "name": "Jupiter",
            "radius": 69911.0,
            "distance": {
                "perihelion": 740520000,
                "aphelion": 816620000
            },
            "gravity": 2.528
        },
        "saturn": {
            "name": "Saturn",
            "radius": 58232.0,
            "distance": {
                "perihelion": 1352550000,
                "aphelion": 1514500000
            },
            "gravity": 1.065
        },
        "uranus": {
            "name": "Uranus",
            "radius": 25362.0,
            "distance": {
                "perihelion": 2742129000,
                "aphelion": 3008413100
            },
            "gravity": 0.886
        },
        "neptune": {
            "name": "Neptune",
            "radius": 24622.0,
            "distance": {
                "perihelion": 4459512500,
                "aphelion": 4537303400
            },
            "gravity": 1.14
        }
    },
    "star": {
        "sun": {
            "name": "Sun",
            "radius": 695700.0,
            "gravity": 27.940
        }
    },
    "dwarf": {
        "pluto": {
            "name": "Pluto",
            "radius": 1188.3,
            "distance": {
                "perihelion": 4436800000,
                "aphelion": 7375900000
            },
            "gravity": 0.620
        }
    }
}

想要访问文件中的earth的半径radius，其表达式写为：

myDate = footage("Exanmle JSON File.json").sourceDate;
myDate.planet.earth.radius

这是一个动态链接，修改json文件中的值，AE中会同时更改。

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